This is a joint request by Group Health Cooperative (GHC) and the Fred Hutchinson Cancer Research Center for a cooperative agreement to support a clinical center in the proposed multi-institutional low dietary fat intervention study to reduce breast cancer incidence in high risk women. The clinical center will be within GHC. Two hundred high risk women will be randomized into the trial. The intervention group will receive training in the low fat diet, followed by intensive counseling in their homes to ensure high compliance. The control group will receive usual care. Follow-up of both groups will occur at 5 months post entry and then yearly. Breast cancer incidence will be monitored by mammography; diet will be monitored by self-report and biochemical measures. During the feasibility phase (year 1), we will determine participation rates, compliance rates, and adverse effects and we will investigate methods to improve compliance, to improve the intervention, and to improve monitoring of the diet. The investigation has arranged to sub-contract with the Northwest Lipid Research Clinic for dietary consultants to prepare instructional materials, train GHC nutrition and counseling staff, provide dietary questionnaires, analyze dietary data and monitor dietary intervention if the need arises. The clinic will also provide biochemical lipid analyses on either a short or long term basis if there is a need for local expertise in this area.